1. Technical Field
The present invention relates to a screw that is not provided with a fastening means such as a fastening recess on the body head.
Priority is claimed on Japanese Patent Application No. 2004-173020, filed Jun. 10, 2004, the content of which is incorporated herein by reference.
2. Background Art
Conventionally, a screw is widely used as a means for joining structural members of a given device. As a means for fastening a screw, a recess such as a plus (+)-shaped “cross recess” or a minus (−)-shaped “slot” is ordinarily formed in the top portion of the screw head, so that fitting a screwdriver having a corresponding tip shape in the recess applies running torque to the screw.
However, a screw that is fastened in a structural element can be readily loosened with a screwdriver having a tip shape that corresponds to the recess. This characteristic is extremely unsuitable when disadvantages arise by loosening of screws by a third party that have been attached in a formal process, for example, when not removing screws serves as a condition for a product warranty.
For this reason, the use of recesses including general shapes such as a cross recess or a slot or the like is conventionally avoided, with screws provided with a specially shaped recess on the top portion of the screw head being used. However, if there is a person in possession of a screwdriver having a tip shape that corresponds to the special recess, then the possibility remains that the screw will be loosened. Therefore, it can be said to be impossible to completely prevent a screw loosening operation due to tampering or the like simply with a recess shape contrivance.
In order to solve such problems, a “security screw” has been proposed as disclosed for example in Patent Document 1. This security screw has a tab for screw fastening that cannot be separated by hand, with the tab being formed in advance on the top portion of the screw head by methods such as integral molding, welding or adhesion and the like. After completion of the screw fastening operation with respect to a structural member, the tab is capable of being separated by a simple tool such as a driver, wrench or pliers. That is, by removing the tab of this security screw after the screw fastening operation, the means (tab) for screw loosening, which serves as a cause for tampering or the like, is proactively eliminated.    Patent Document 1: Japanese Unexamined Patent Application, First Publication No. 2003-074531